The present invention relates to a light-sensitive material, especially a photopolymerizable material, for producing color-test films for multi-color printing. It also relates to a color test method, in which a multi-color image is produced on an image-receiving material from a plurality of part-color images in register. The part-color images are produced by laminating a photopolymerizable layer colored in a main color to the image-receiving material, exposing under the respective color separation, developing the image by peeling off the base film of the photopolymerizable layer together with the non-image areas and repeating the same steps using a photopolymerizable layer in a different main color.
A color test method and a material therefor are known from U.S. Pat. No. 4,895,787. The material is composed of a transparent base film, the surface of which preferably has been pretreated for adhesion promotion, a photopolymerizable layer that contains a dye or a colored pigment in a main color of the multi-colored print, and an adhesion layer, that can be activated by heating, on the photopolymerizable layer. After lamination to an image-receiving material and exposure through the base film, the material is developed by peeling apart the base film and the image-receiving material. The exposed areas of the light-sensitive color layer remain on the base film, and the unexposed areas together with the complete adhesion layer remain on the image-receiving material. The method thus works positively, i.e., a positive image of the original is produced on the image-receiving material.
This processing method has the great advantage that it requires no alkaline or acidic solutions and no organic solvents for development, so that no disposal of these is required. A disadvantage of this method is its lower resolution as compared with a developing method using solutions.
The material properties that affect the resolving power have been investigated and described in a publication by J. H. Choi, J. of Im. Tech., 15(4): 190 (1989). Essentially, these properties are the adhesion forces
(a) between the unexposed areas of the photopolymerizable color layer and the base film, PA1 (b) between the exposed areas of the photopolymerizable color layer and the base film, PA1 (c) between the unexposed areas of the photopolymerizable color layer and the adhesion layer, and PA1 (d) between the exposed areas of the photopolymerizable color layer and the adhesion layer, and the cohesion forces PA1 (e) within the photopolymerizable color layer, and PA1 (f) within the adhesion layer. PA1 (A) a transparent flexible base film of a plastic, PA1 (B) a photopolymerizable layer containing PA1 (C) a thermoplastic adhesion layer on the light-sensitive layer.
The cohesion forces are generally greater than the adhesion forces, but at least greater than the smallest adhesion force in each case. The adhesion force between the adhesion layer and the image-receiving material should likewise be greater than all the other adhesion forces.
A further disadvantage of the known material is its unacceptably low storage stability in many cases. If the material is stored at room temperature in the unexposed state for several weeks, it changes its properties so that the image reproduction after exposure and development deteriorates. This manifests itself in visible defects in the half-tone images, caused by inaccurate tearing out or tearing apart of screen dots. At elevated temperature, this change is observed after one day or a few days.
EP 339,860 discloses a color test method using a material of similar structure, composed of a base film, a light-sensitive pigment-containing layer and an adhesion layer. The individual part-color images are produced by washing out the non-image areas with a developer. Of course, in this method the adhesion of the individual layers does not play the same role as in a peel-apart method. In this case, a polyvinyl ether is added as a plasticizer to the adhesion layer.